Camera and wide-angle field distance-measuring camera

ABSTRACT

A camera includes a sensor array which can detect a brightness signal of a subject and has a plurality of segments for focal point detection, a first photometry unit for calculating the brightness signal of the subject on the basis of an output of one segment or outputs of the segments of the sensor array, a second photometry unit which can detect a brightness signal of the subject in a detection range wider than that for the detection of the subject brightness signal by the sensor array, and a determination unit for determining on the basis of an output of the second photometry unit whether the use of the first photometry unit is forbidden. The camera can determine backlight without any inconvenience even on photographing condition close to the very limit of a photometrical range.

This application is a Divisional application of U.S. application Ser.No. 10/449,561, filed May 30, 2003, which claims the benefit of JapaneseApplications No. 2002-163082, filed in Japan on Jun. 4, 2002 and No.2002-192447 filed in Japan on Jul. 1, 2002, the entire contents of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to cameras, and more particularly to acamera having a backlight determination function and a wide-angle fielddistance-measuring camera having a passive auto-distance-measuringdevice that is used in cameras and video cameras and the like.

2. Related Art Statement

As cameras having a backlight determination function, a camera whichmeasures the brightness of a primary subject using a photometric sensorto detect backlight has been known.

As the cameras having a backlight determination function, an area AFcamera is known. In the area AF camera, the brightness of a primarysubject, selected by an AF sensor, is measured using the AF sensor andthe obtained brightness is compared to the average brightness obtainedby an AE sensor, thus determining backlight.

In this type of camera, different sensors from the AF sensor and the AEsensor are used in order to accomplish the original objective of the AFsensor and that of the AE sensor. A dynamic range required forphotometry is fairly large. Accordingly, in many cases, the respectivesensors are generally designed so as to have sensitivity fairly close tothe maximum dynamic range necessary for photographing.

In the above-mentioned camera based on the conventional techniques, thetwo different sensors necessarily have different photometricallypossible ranges.

Particularly, many AF sensors generally use a method for integrating aphotoelectric current of the sensor and obtaining the brightness of asubject on the basis of the time that elapsed before the integratedvalue reaches a threshold level. Accordingly, if the brightness is high,the photoelectric current is large, the time that elapsed before theintegrated value reaches the threshold level is short, and aphotometrical range for the high brightness is small.

In this instance, under photographing conditions that are fairly closeto the maximum possible photometrical range or exceeding this range,backlight cannot be detected with accuracy. Disadvantageously, incorrectbacklight detection is caused.

For example, for a subject area where the brightness of a subjectexceeds the limit value of brightness which the AF sensor can measurebut the subject brightness lies within a possible photometrical range ofthe AE sensor, the AF sensor exceeds the limit value of photometry.Consequently, the AF sensor outputs data which is different from theactual brightness of the subject, resulting in incorrect backlightdetection. Although there is no backlight in fact, the camera maydetermine backlight by mistake.

On the other hand, AF cameras with a passive auto-distance-measuringdevice have been well-known. When this type of camera photographs abacklight scene or a scene in a nightscape as a background, integralaction for measuring distance is performed using a high-brightness areaof the background or a light source as a reference. Accordingly, aproper image signal of a person serving as a primary subject cannot beobtained. Disadvantageously, the person is out of focus but thebackground is in focus.

In order to overcome the above disadvantages, according to adistance-measuring method disclosed in Japanese Unexamined PatentApplication Publication No. 5-264887, backlight is detected usingphotometric data and data of a distance-measuring sensor and, when abacklight mode is detected, a monitor area to monitor subject-brightnessinformation, which is used for integral action, is set at the center ofa capturing area. Alternatively, integration is performed using an areahaving the lowest integral speed of a plurality of preset monitor areasas a reference. Thus, poor auto-distance-measuring for the primarysubject in the backlight mode is improved.

According to a distance-measuring method disclosed in JapaneseUnexamined Patent Application Publication No. 7-199039, a nightscapemode for nightscape photographing is provided. When the nightscape modeis set, whether auxiliary light is needed is determined. When it isdetermined that brightness is low, auxiliary light is emitted to improvepoor auto-distance-measuring in the nightscape photographing.

For the distance-measuring method disclosed in Japanese UnexaminedPatent Application Publication No. 5-264887, however, when thehigh-brightness area of the background includes spotted light reflectedby an object with high reflectivity, or when a primary subject such as aperson exists on a position other than the center of the capturing area,backlight cannot be detected or image signals of a primary subject issaturated, so that the subject image which is out of focus may becaptured.

For the distance-measuring method disclosed in Japanese UnexaminedPatent Application Publication No. 7-199039, when a light source isbright in a nightscape as a background, auxiliary light may not beemitted. If the auxiliary light is emitted, in some cases, the amount oflight may be insufficient and the effect of the auxiliary light may notbe derived sufficiently.

In consideration of the above disadvantages, Japanese Unexamined PatentApplication Publication No. 2001-141987 discloses that a first integralis performed on condition that a monitor area is set wider thanconventional monitor areas, when the contrast of a low brightness areain output data of line sensors obtained by a first integral is low, thelow brightness area is set to a monitor area, and a second integral isperformed to this area. When a backlight scene is photographed or ascene in a nightscape as a background is photographed, image signals ofa person serving as a primary subject can be obtained.

When a taking lens with a wide-angle focal length is used, adistance-measuring area is formed with a wide angle. Therefore, in somecases, the line sensors are used from end to end. Accordingly, due tothe influence of a deterioration in the performance of reception lensesof an AF sensor or a degradation in the sensitivity of the line sensors,the end portions of each line sensor generate output data indicatinglower brightness than that indicated by data generated from the centralportion of each line sensor.

FIG. 24 shows output data of line sensors when a uniform brightness areais monitored. FIG. 24 shows the fact that the respective end portions ofthe line sensors generate data indicating brightness darker than thatindicated by data of the central portions thereof. In this case, whendistance-measuring control is performed according to a method disclosedin Japanese Unexamined Patent Application Publication No. 2001-141987,it is determined by mistake that output data of the end portions of theline sensors indicates low brightness. Disadvantageously, photographingis performed with poor distance-measuring.

SUMMARY OF THE INVENTION

The present invention is made in consideration of the abovecircumstances. It is an object of the present invention to provide acamera having a system for detecting backlight using an AF sensor and anAE sensor. In the camera, when a photometrical value obtained by atleast one sensor is equal to or larger than predetermined brightness,backlight detection is not performed. Accordingly, even underphotographing condition close to the maximum possible photometric rangeof one sensor, backlight determination can be performed without anyinconvenience.

Another object of the present invention is to provide a wide-angle fielddistance-measuring camera with a distance-measuring device which canmeasure the distance to a primary subject with reliability independentlyof the condition of a high brightness area of a background when abacklight scene or a scene in a nightscape as a background isphotographed using a wide-angle lens.

According to the present invention, there is provided a cameraincluding: a sensor array which can detect a brightness signal of asubject and has a plurality of segments for focal point detection; afirst photometry means for calculating the brightness signal of thesubject on the basis of an output of one segment or outputs of thesegments of the sensor array; a second photometry means which can detecta brightness signal of the subject in a detection range wider than thatfor the detection of the subject brightness signal by the sensor array;and a determination means for determining on the basis of an output ofthe second photometry means whether the use of the first photometrymeans is forbidden. AF-sensor spot is forbidden in accordance withbrightness measured by photometric sensors.

According to the present invention, there is provided a cameraincluding: an exposure means which is used in photographing a subject; asensor array which can detect a brightness signal of the subject and hasa plurality of segments for focal point detection; a first photometrymeans for calculating the brightness signal of the subject on the basisof an output of one segment or outputs of the segments of the sensorarray; a second photometry means which can detect a brightness signal ofthe subject in a detection range wider than that for the detection ofthe subject brightness signal by the sensor array; and a determinationmeans for determining, in accordance with a result of determination ofwhether the difference between the brightness signals obtained by thefirst and second photometry means is larger than a predetermined value,whether exposure used in photographing the subject is changed, whereinthe determination means changes the determination regarding the exposurein accordance with an output of the first photometry means. In otherwords, a threshold level used in backlight determination is changed inaccordance with brightness measured by photometric sensors.

According to the present invention, there is provided a wide-angle fielddistance-measuring camera having a distance-measuring device, thedistance-measuring device including: a pair of reception lenses forforming an image of a subject on a pair of line sensors; the pair ofline sensors for converting the subject image formed by the receptionlenses into electric signals in accordance with the intensity of light;an integral control means for performing integral control of the pair ofline sensors; a calculation means for calculating data corresponding toa camera-to-subject distance on the basis of subject image datagenerated from the pair of line sensors. The distance-measuring devicefurther includes: a monitor means for monitoring subject-brightnessinformation used in the integral control; a monitor control means forsetting a monitor area and outputting monitor data; and alow-brightness-area determination means for determining a low brightnessarea included in output data of the line sensors in consideration of theinfluence of a deterioration in the performance of the reception lensesor a degradation in the sensitivity of the sensors, with the output databeing obtained by integral. The low-brightness-area determination meanschanges a threshold value used in determination of the low brightnessarea in the output data in the central portion of each line sensor andthe peripheral portions thereof. The low-brightness-area determinationmeans approximates a threshold value used in determination of the lowbrightness area in the output data of the line sensors with a high-ordercurve. Further, the low-brightness-area determination means corrects theoutput data of the line sensors by the amount as much as the influenceof the deterioration in the performance of the reception lenses or thedegradation in the sensitivity of the sensors, and then determines a lowbrightness area.

Other features and advantages of the present invention will becomeapparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the structure of an essential part ofa camera according to a first embodiment of the present invention;

FIG. 2 is a diagram showing the relationship between a capturing fieldof view and a distance-measuring field of view in the camera of FIG. 1;

FIG. 3A is a diagram showing the structure of each sensor array(distance-measuring sensor) in the camera of FIG. 1 and adistance-measuring field-of-view area (monitor area) in a wide-anglemode;

FIG. 3B is a diagram showing a distance-measuring field-of-view area ina telephoto mode of each sensor array (distance-measuring sensor) in thecamera of FIG. 1;

FIG. 3C is a diagram showing image data obtained in correspondence todistance-measuring points captured by the sensor arrays(distance-measuring sensors) in the camera of FIG. 1;

FIG. 4 is a graph showing the relationship between brightness BVSPmeasured by distance-measuring sensors, brightness BVAVG measured byphotometric sensors, and stroboscopic light emission in executing aphotographing sequence of FIG. 5, which will be described later;

FIG. 5 is a flowchart of the photographing sequence in the applicationof a zoom lens camera capable of changing a focal length in a range of35 mm to 80 mm as the camera of FIG. 1;

FIG. 6 is a graph explaining the relationship between the brightnessBVSP measured by the distance-measuring sensors, the brightness BVAVGmeasured by the photometric sensors, and the stroboscopic light emissionin executing a photographing sequence of FIG. 7, which will be describedlater;

FIG. 7 is a flowchart of a modification example of the photographingsequence in the application of a zoom lens camera capable of changing afocal length in a range of 35 mm to 80 mm as the camera of FIG. 1according to the first embodiment;

FIG. 8 is a block diagram showing the structure of a distance-measuringdevice built in a wide-angle field distance-measuring camera accordingto a second embodiment of the present invention;

FIG. 9 is a diagram showing an example of setting of a monitor area forfirst integral and a calculation area in the distance-measuring deviceof FIG. 8;

FIG. 10 is a diagram showing an example of setting of a monitor area forsecond integral and a calculation area in the distance-measuring deviceof FIG. 8;

FIG. 11 is a diagram showing an example of setting of the monitor areafor second integral and increased calculation areas in thedistance-measuring device of FIG. 8;

FIG. 12 is a view showing a photographing scene of the wide-angle fielddistance-measuring camera according to the second embodiment of thepresent invention;

FIG. 13 is a graph showing subject image data obtained by integratingthe photographing scene of FIG. 12 according to the first integral;

FIG. 14 is a graph showing subject image data obtained by integratingthe photographing scene of FIG. 12 according to the second integral;

FIG. 15 is an electric circuit diagram showing a monitor circuit of thedistance-measuring device in the wide-angle field distance-measuringcamera according to the second embodiment of the present invention;

FIG. 16 is a diagram showing an example of a method for setting amonitor area in the wide-angle field distance-measuring camera accordingto the second embodiment of the present invention;

FIG. 17 is a diagram showing another example of the method for setting amonitor area in the wide-angle field distance-measuring camera accordingto the second embodiment of the present invention;

FIG. 18 is a flowchart of a distance-measuring sequence of thedistance-measuring device in the wide-angle field distance-measuringcamera according to the second embodiment of the present invention;

FIG. 19 is a flowchart of a “low-brightness and low-contrast”determination sequence in the distance-measuring sequence of FIG. 18;

FIG. 20 is a graph showing output data of line sensors of adistance-measuring device in a wide-angle field distance-measuringcamera according to a third embodiment of the present invention;

FIG. 21 is a graph showing output data of line sensors of adistance-measuring device in a wide-angle field distance-measuringcamera according to a fourth embodiment of the present invention;

FIG. 22 is a flowchart of a distance-measuring sequence using athreshold line as a high-order curve in the distance-measuring device ofthe wide-angle field distance-measuring camera according to the thirdembodiment of the present invention;

FIG. 23 is a flowchart of a distance-measuring sequence of correctingsensor output data to perform correct distance-measuring in thedistance-measuring device of the wide-angle field distance-measuringcamera according to the fourth embodiment of the present invention; and

FIG. 24 is a graph showing sensor output data obtained by capturing auniform brightness area through a sensor of a conventional camera.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described hereinbelowwith reference to the drawings.

FIG. 1 is a block diagram showing the structure of an essential part ofa camera according to a first embodiment of the present invention.

FIG. 1 shows the block diagram of a lens-shutter type silver-halide filmcamera for photographing an subject image captured by a taking lens 8 ona film 10 by opening or closing a shutter 19.

According to the present embodiment, the camera has a CPU 1 forcontrolling the whole camera. The CPU 1 serves as control meanscomprising, for example, a one-chip microcomputer for controlling all ofsequences of the camera. The CPU further includes: first photometrymeans for calculating a brightness signal of a subject on the basis ofoutputs of sensor arrays 3 a and 3 b, which will be described later; anddetermination means for determining on the basis of an output of secondphotometry means, which will be described later, whether the use of anoutput of the first photometry means is forbidden.

The CPU 1 performs a process of executing a predetermined photographingsequence in accordance with control of switch input means 13 through aphotographer.

Distance-measuring means for measuring the distance to a subject 17comprises: two reception lenses 2 a and 2 b, the pair of sensor arrays(distance-measuring sensors) 3 a and 3 b, and A/D conversion means 4.Subject image signals, obtained through the two reception lenses 2 a and2 b disposed at a distance of a base length B from each other, arephotoelectrically converted by the pair of sensor arrays 3 a and 3 b,and the resultant signals are analog-to-digital converted into digitalimage signals by the A/D conversion means 4.

The CPU 1 compares this pair of digital image signals to obtain arelative parallax X between the image input signals.

In other words, the relative parallax X varies such that X=B×F/L,wherein a camera-to-subject distance is L, a focal length of thereception lenses 2 a and 2 b is F, and the foregoing base length is B.Accordingly, when the parallax X is detected, the distance-measuringdistance L can be calculated by the CPU 1.

The sensor arrays 3 a and 3 b are, for example, non-TTL-AF type. Thesensor arrays 3 a and 3 b are laterally arranged in the camera. When asubject scene is photographed as shown in FIG. 2, the sensor arrays 3 aand 3 b monitor an area 23 a.

As shown in FIG. 3A, the whole monitor area 23 a is divided into 13blocks. The above-mentioned parallax X is detected using image signalscorresponding to the respective blocks, so that distances of 13 pointsin a capturing area can be measured.

For 13 distance-measuring signals obtained as mentioned above, thedistance-measuring signal indicating, for example, the shortestdistance, denotes a camera-to-primary-subject distance.

A photographing optical system including the taking lens 8 serving as azoom lens, the reception lenses 2 a and 2 b included in adistance-measuring optical system, and an AE lens 5 included in aphotometric optical system are arranged separately from each other.

When the photographer controls an operating member (not shown), the CPU1 controls a zoom driving circuit 14 to drive the taking lens 8 in orderto shift the focal length of the taking lens 8 from a wide-angle mode toa telephoto mode, so that a capturing angle of field and a capturingfield of view can be changed.

This camera has a finder optical system 20 through which thephotographer confirms a capturing area.

The finder optical system 20 is constructed so as to operate inaccordance with the focal length of the taking lens 8.

In other words, when the CPU 1 controls the zoom driving circuit 14 toshift the focal length of the taking lens 8 from the wide-angle mode tothe telephoto mode, the finder optical system 20 is also driven. Thus,the focal length is shifted from the wide-angle mode to the telephotomode.

The camera is designed such that a finder field of view is the same asthe field of view of the taking lens 8 independently of the focallength. When the photographer looks through the finder optical system20, he or she can recognize a capturing range (field of view).

As mentioned above, the photographing optical system and thedistance-measuring optical system are arranged separately from eachother. For example, when the taking lens 8 is arranged in the wide-anglemode, the capturing field of view is shown by reference numeral 24W inFIG. 2 and the field-of-view area of the sensor arrays 3 a and 3 b isshown by reference numeral 23 a.

When the taking lens 8 is arranged in the telephoto mode, the capturingfield is shown by reference numeral 24T in FIG. 2. On the other hand,the distance-measuring optical system includes the fixed lenses which donot move in accordance with the focal length of the taking lens 8.Therefore, the field-of-view area of the sensor arrays 3 a and 3 b isnot changed. The relationship between the capturing field and thedistance-measuring field-of-view area is shown by the relationshipbetween 24T and 23 a.

When the capturing field is shown by 24W in FIG. 2, multi-point AF(multi-AF) with 13 points is performed in the field shown by the area 23a including the 13 blocks of each of the sensor arrays(distance-measuring sensors) 3 a and 3 b. As shown in FIG. 3A, each ofthe sensor arrays 3 a and 3 b is composed of 13 sensor segments A1 toA13 each having a plurality of pixels.

When the capturing field is shown by 24T in FIG. 2, as shown in FIG. 3B,7-point AF (multi-AF) is performed in a distance-measuring area 23 b,namely, using seven segments of the 13 segments of each of the sensorarrays 3 a and 3 b.

Referring to FIG. 1, split type photometric sensors 6 a and 6 b forreceiving light which passes through the AE lens 5 are included insecond photometry means.

Outputs of the photometric sensors 6 a and 6 b are converted by an AEcircuit 21 comprising a logarithmic compression circuit, the AE circuit21 being included in the second photometry means. Thus, brightness inthe capturing area is measured. On the basis of the brightness, the CPU1 performs exposure control.

The photometric optical system is separated from the optical systemincluding the taking lens 8 and does not operate in interlocking withthe focal length of the taking lens 8.

Accordingly, the field of view obtained when the taking lens 8 isarranged in the wide-angle mode is set to 24W, that obtained when thetaking lens 8 is arranged in the telephoto mode is set to 24T. FIG. 2shows the correspondence between the fields 24W and 26 b of thephotometric sensor 6 b and between the fields 24T and 26 a of thephotometric sensor 6 a.

Therefore, when the taking lens 8 is disposed in the telephoto mode, theoutputs of the sensor 6 a are used. When the taking lens 8 is arrangedin the wide-angle mode, the sum of the outputs of the respective sensors6 a and 6 b is used. Thus, photometry in substantially the same range asthe capturing field can be performed.

As shown in FIGS. 3A and 3B, the sensor arrays 3 a and 3 b each have the13 sensor segments A1 to A13, obtained by dividing each sensor arrayinto 13 segments, and each segment has strip pixels corresponding to adistance-measuring point. Since each pixel outputs data corresponding toshades of an image, image data is obtained as shown in FIG. 3C.

When image outputs obtained as mentioned above are averaged, the averagebrightness of the respective distance-measuring points can be obtained.

In the above-mentioned structure, the position of a primary subject canbe detected with multi-AF. In addition, brightness at the positionthereof can be obtained. Consequently, on the basis of a process flow asshown in FIG. 5, which will be described in detail later, photographingputting weight on the primary subject can be realized by exposurecontrol.

The photometry process using the distance-measuring sensors (sensorarrays) 3 a and 3 b will be described in detail later.

On the basis of a distance-measured result by the multi-AF, the CPU 1controls the taking lens 8 via a taking-lens control circuit (LD) 9 tofocus on a subject, and opens or closes the shutter 19 on the basis ofthe photometry result obtained by the distance-measuring sensors 3 a and3 b and the photometry result obtained by the photometric sensors 6 aand 6 b. Thus, photographing due to exposure control putting weight onthe primary subject can be realized.

In the exposure control, the CPU 1 controls a flash circuit 15 to emitstroboscopic light 16 as necessary.

A concrete example of a zoom lens camera capable of changing a focallength in a range of 35 mm to 80 mm and having the above-mentionedstructure will now be described with reference to FIGS. 4 and 5.

FIG. 5 is a flowchart explaining a concrete photographing sequence.

FIG. 4 is a graph explaining the relationship between brightness BVSPmeasured by the sensor arrays (distance-measuring sensors), brightnessBVAVG measured by the photometric sensors, and the stroboscopic lightemission in execution of the photographing sequence of FIG. 5.

When a photographer controls the operating member 13, the photographingsequence of FIG. 5 is started under the control of the CPU 1.

In step S101, a zoom position is detected, thus detecting to which focallength the taking lens 8 is currently set.

In step S102, the focal length detected in step S101 is stored in avariable ZM.

In step S103, whether the focal length of the taking lens 8 is longerthan 50 mm so as to be in the telephoto mode is determined on the basisof the variable ZM. If the focal length thereof is in the telephotomode, the sequence proceeds to step S104. If the focal length is in thewide-angle mode, i.e., 50 mm or less than 50 mm, the sequence proceedsto step S105.

In step S104, since the focal length of the taking lens 8 is in thetelephoto mode, only the outputs of the foregoing photometric sensor 6 ais used in average photometry. The average brightness of the wholecapturing area obtained from the outputs of the photometric sensor 6 ais stored in a variable BVAVG.

In step S105, since the focal length of the taking lens 8 is in thewide-angle mode, the average value of the outputs of the foregoingphotometric sensors 6 a and 6 b is used in the average photometry. Theaverage brightness of the whole capturing area obtained from the outputsof the photometric sensors 6 a and 6 b is stored in a variable BVAVG.

In steps S106 and S107, when the focal length is in the wide-angle mode,distance-measuring points corresponding to the 13 sensor segments areused. When the focal length is in the telephoto mode, sevendistance-measuring points are used. A distance-measuring point which isaround a primary subject is selected from those distance-measuringpoints (the detailed description is omitted because it is included inthe explanation regarding FIGS. 1 and 3). The distance between thecamera and the primary subject is calculated using the sensor arrays(distance-measuring sensors) which are around a point of the primarysubject.

In step S108, the distance-measuring point of the primary subject isstored in a variable n (in this case, since there are 13distance-measuring points, n denotes any of 1 to 13).

In step S109, the brightness of an area around the primary subject ismeasured using the sensor segments of the distance-measuring sensors 3 aand 3 b, which are around the primary subject.

In other words, since the variable n denotes n-th sensor segment in eachdistance-measuring sensor, the n-th segment corresponding to thedistance-measuring point closest to the primary subject, the brightnessof the n-th point sensor segment of each of the AF sensors is measured.

In step S110, the spot brightness of the primary subject, obtained inthe primary subject photometry in step S109, is stored in a variableBVSP.

In step S111, the taking lens 8 is driven such that the subject isfocused on the camera-to-subject distance obtained in step S106.

In step S112, on the basis of the average brightness of the wholecapturing area obtained in step S104 or S105, whether the capturing areais dark and emission of the stroboscopic light 16 is needed isdetermined.

Specifically, BVAVG is compared to hand movement brightness whichchanges in accordance with the focal length. When BVAVG is lower thanthis brightness, the sequence proceeds to step S116. If NO, the sequenceproceeds to step S113.

In step S113, whether the average brightness of the whole capturing areaobtained in step S104 or S105 is equal to or higher than predeterminedbrightness is determined.

Specifically, BVAVG is compared to predetermined brightness BV (BV13).When BVAVG is lower than the predetermined brightness, the sequenceproceeds to step S114. If NO, the sequence proceeds to step S115.

In this instance, according to the present embodiment, the photometrypossible range of the distance-measuring sensors 3 a and 3 b includesBV2 to BV13 (corresponding to EV7 to EV18 obtained by converting BV2 toBV13 into EV values in the case of ISO 100).

When high brightness exceeding BV13 is incident, the distance-measuringsensors 3 a and 3 b output indeterminate values.

In the case of the high brightness, when the values of the spotdistance-measuring sensors 3 a and 3 b are used in photometry forbacklight detection, in the same way as step S113, whether the outputsof the distance-measuring sensors 3 a and 3 b are used in photometry isdetermined in accordance with the value BVAVG based on the outputs ofthe photometric sensor 6 a or the sum of the outputs of the photometricsensors 6 a and 6 b, thus controlling such that the photometrical valueexceeding the photometrically possible range of the distance-measuringsensors 3 a and 3 b is not used (a control process by the determinationmeans built in the CPU 1).

In step S114, whether backlight is detected is determined on the basisof the brightness of the primary subject obtained in step S110 and theaverage brightness of the whole capturing area obtained in steps S104 orS105.

Specifically, BVAVG-BVSP is performed. When the brightness difference islarger than one scale, it is determined that backlight is detected. Thesequence proceeds to step S116. If NO, the sequence proceeds to stepS115.

In step S115, the shutter is controlled on the basis of an aperturescale according to the brightness BVAVG to expose the film 10.

In step S116, the shutter is controlled on the basis of the aperturescale according to the brightness BVAVG or the hand movement brightnessto expose the film 10. Further, in order to perform the exposureappropriate to a backlighted subject, or in order to correct a darkcapturing area, the stroboscopic light 16 is emitted by the flashcircuit 15.

In step S117, since the exposure of the film 10 is completed, the film10 is wound by one frame. The sequence is terminated.

FIG. 4 shows the relationship among the brightness BVSP measured by thedistance-measuring sensors 3 a and 3 b, the brightness BVAVG measured bythe photometric sensors 6 a and 6 b, and the stroboscopic light emissionin accordance with the sequence shown in FIG. 5. In FIG. 4, the abscissaaxis denotes the brightness BVAVG measured by the photometric sensors 6a and 6 b. The ordinate axis denotes the brightness BVSP of the primarysubject measured by the distance-measuring sensors 3 a and 3 b.

Referring to FIG. 4, an area A denotes a low-brightness auto-flash areain which stroboscopic light is emitted on the basis of the determinationof low brightness in step S112 mentioned above.

An area B denotes a backlight auto-flash area in which stroboscopiclight is emitted on the basis of the determination of backlight in stepS114 mentioned above.

An area C denotes a non-flash area in which stroboscopic light is notemitted on the basis of the determination of whether backlight detectionis performed in step S113 mentioned above.

In the above concrete example, whether brightness lies within a rangewhere the distance-measuring sensors 3 a and 3 b can be used to measurebrightness is determined on the basis of the photometrical valueobtained by the photometric sensors 6 a and 6 b. Accordingly, thedistance-measuring sensors 3 a and 3 b are not used when brightnessexceeds the distance-measuring-sensor applicable range. Thus, incorrectbacklight determination is not performed.

A modification example of the photographing sequence according to theabove-mentioned embodiment will now be described hereinbelow withreference to FIGS. 6 and 7. In this modification, a zoom lens camerawhich can change a focal length in a range of 35 mm to 80 mm issimilarly used.

FIG. 7 is a flowchart explaining the photographing sequence as themodification. FIG. 6 shows the relationship among the brightness BVSPmeasured by the distance-measuring sensors, the brightness BVAVGmeasured by the photometric sensors, and the stroboscopic light emissionin the photographing sequence as the modification of FIG. 7.

When a photographer first controls the operating member 13, thephotographing sequence of FIG. 7 is started under the control of the CPU1.

In step S200, the ISO sensitivity of the film 10 is detected. Thedetected sensitivity is converted into an SV value. The SV value isstored in a variable SV.

In step S201, a zoom position is detected, thus detecting to which focallength the taking lens 8 is currently set.

In step S202, the focal length detected in step S201 is stored in avariable ZM.

In step S203, whether the focal length of the taking lens 8 is longerthan 50 mm so as to be in the telephoto mode is determined on the basisof the variable ZM. If the focal length is in the telephoto mode, thesequence proceeds to step S204. If the focal length is in the wide-anglemode, i.e., 50 mm or less than 50 mm, the sequence proceeds to stepS205.

In step S204, since the focal length of the taking lens is in thetelephoto mode, only the output of the foregoing photometric sensor 6 ais used as photometric sensor in average photometry.

The average brightness of the whole capturing area obtained from theoutput of the photometric sensor 6 a is stored in a variable BVAVG.

In step S205, since the focal length of the taking lens is in thewide-angle mode, the average value of the respective outputs of theforegoing photometric sensors 6 a and 6 b are used as photometric sensorin the average photometry.

The average brightness of the whole capturing area obtained from theoutputs of the photometric sensors 6 a and 6 b is stored in a variableBVAVG.

In step S206, a distance-measuring point which is near a primary subjectis selected from 13 distance-measuring points (the detailed descriptionhas been made in the explanation regarding FIGS. 1 and 3).

In step S207, the camera-to-subject distance is calculated using thesensor segments in the vicinity of the point around the primary subject.

In step S208, the distance-measuring point closest to the primarysubject is stored in a variable n (in this case, since there are 13distance-measuring points in the wide-angle mode and there are sevendistance-measuring points in the telephoto mode, n denotes any value of1 to 13).

In step S209, the brightness of an area around the primary subject ismeasured using outputs of the sensor segments of the distance-measuringsensors, the sensor segments corresponding to the distance-measuringpoint n closest to the primary subject.

In step S210, the spot brightness of the primary subject, obtained usingthe sensor segments corresponding to the distance-measuring point n inthe primary subject photometry, is stored in a variable BVSP.

In step S211, the taking lens 8 is driven via the taking-lens drivingcircuit (LD) 9 so that the subject is focused on the camera-to-subjectdistance obtained in step S207.

In step S212, on the basis of the average brightness of the wholecapturing area obtained in step S204 or S205, whether the capturing areais dark and the emission of the stroboscopic light 16 is needed isdetermined.

Specifically, a hand movement EV value based on the focal length iscompared to the sum of BVAVG and SV. If the sum of BVAVG and SV issmaller than the EV value, the sequence skips to step S218. If NO, thesequence proceeds to step S213.

In step S213, whether the average brightness of the whole capturing areaobtained in step S204 or S205 is equal to or larger than predeterminedbrightness is determined.

Specifically, BVAVG is compared to the predetermined brightness BV13. IfBVAVG is larger than BV13, the sequence proceeds to step S214. If NO,the sequence proceeds to step S215.

In step S214, whether backlight is detected is determined on the basisof the brightness of the primary subject obtained in step S210 and theaverage brightness of the whole capturing area obtained in S204 or S205.

Specifically, BVAVG-BVSP is calculated. When the brightness differenceis larger than two scales, it is determined that backlight is detected.The sequence proceeds to step S218. If NO, the sequence proceeds to stepS217.

In step S215, whether the average brightness of the whole capturing areaobtained in step S204 or S205 is equal to or larger than thepredetermined brightness is determined.

Specifically, BVAVG is compared to predetermined brightness BV5. IfBVAVG is larger than BV5, the sequence proceeds to step S216. If NO, thesequence proceeds to step S214.

In step S216, whether backlight is detected is determined on the basisof the brightness of the primary subject obtained in step S210 and theaverage brightness of the whole capturing area obtained in step S204 orS205.

Specifically, BVAVG-BVSP is calculated. If the brightness difference islarger than one scale, it is determined that backlight is detected. Thesequence proceeds to step S218. If NO, the sequence proceeds to stepS217.

In this instance, according to the present embodiment, a range where thedistance-measuring sensors 3 a and 3 b can perform photometry is a rangeof BV0 to BV15 (corresponding to EV5 to EV21 obtained by converting BV0to BV15 into EV values in the case of ISO 100).

However, the distance-measuring sensors 3 a and 3 b have poor linearityin the high brightness side and the low brightness side. In photometryof high brightness exceeding BV13 and low brightness of BV5 or lower,errors increase.

Accordingly, in the photographing sequence according to the presentmodification, when the values of the distance-measuring sensors 3 a and3 b are used in photometry for backlight detection in the case of highbrightness or low brightness, a threshold value used in backlightdetermination is changed as performed in steps S213, S214, S215, andS216. The threshold value used in the backlight determination is changedfrom 1 EV to 2 EV in a range where a photometry error is small. Thus,incorrect backlight determination is not performed on the basis of thephotometry errors of the outputs of the distance-measuring sensors 3 aand 3 b (a control process by the determination means built in the CPU 1according to the present modification).

In step S217, the shutter 19 is controlled with an aperture scale basedon the brightness BVAVG to expose the film 10.

In step S218, the shutter 19 is controlled with an aperture scale basedon the brightness BVAVG, or the shutter 19 is controlled with anaperture scale based on a hand movement EV value, thus exposing the film10. Further, the stroboscopic light 16 is emitted through the flashcircuit 15 in order to correct the exposure with respect to abacklighted primary subject, or in order to correct a dark capturingarea.

In step S219, since the exposure of the film 10 is completed, the film10 is wound by one frame. The sequence is terminated.

FIG. 6 shows the relationship between the brightness BVSP of thedistance-measuring sensors 3 a and 3 b, the brightness BVAVG of thephotometric sensors 6 a and 6 b, and the stroboscopic light emission inthe photographing sequence according to the modification of FIG. 7. InFIG. 6, the abscissa axis denotes the brightness BVAVG measured by thephotometric sensors 6 a and 6 b. The ordinate axis denotes thebrightness BVSP measured by the distance-measuring sensors 3 a and 3 b.

In FIG. 6, areas A and D each denote a low-brightness auto-flash areawhere the stroboscopic light is emitted on the basis of theabove-mentioned low-brightness determination.

According to the present modification, each low-brightness auto-flasharea is calculated on the basis of ISO sensitivity, shutter speedaccording to the focal length due to hand movement, an aperture valueaccording to the focal length.

For example, according to the present modification, in the case of ISO100 and the wide-angle mode, the low-brightness auto-flash areacorresponds to the area D+A below BV5. In the case of ISO 400 and thewide-angle mode, the low-brightness auto-flash area corresponds to thearea A below BV3.

An area B denotes a backlight auto-flash area in which the stroboscopiclight is emitted on the basis of the foregoing backlight determination.

An area C denotes a non-flash area where the stroboscopic light is notemitted on the basis of the above-mentioned low-brightness determinationand backlight determination.

In other words, according to the above modification, the threshold valueto be used in the backlight determination using the photometric sensors6 a and 6 b and the distance-measuring sensors 3 a and 3 b is changed inaccordance with the photometrical value measured by the photometricsensors 6 a and 6 b. Consequently, even in a brightness area where theerror caused by the distance-measuring sensors 3 a and 3 b is large,backlight can be correctly detected.

According to the present embodiment including the modification, each ofthe distance-measuring sensors is divided into 13 segments correspondingto distance-measuring points. When outputs of distance-measuring sensorsdivided according to other various modifications are used in primarysubject photometry, the present invention can also be applied.

According to the present embodiment, the distance-measuring sensorshaving one-dimensional distance-measuring points are used. For instance,when outputs of the multi-distance-measuring sensors capable ofdistance-measuring two-dimensional areas are used in primary subjectphotometry, the present invention can also be applied.

The present embodiment describes the camera using a silver halide filmas an example. The present invention can also be applied to a digitalcamera in which a photographing optical system is different from adistance-measuring optical system.

According to the present embodiment, the photometrical value of theprimary subject is used in backlight detection. The present inventioncan also be applied to a case where only exposure correction isperformed on the basis of, for example, the photometrical value of anarea other than the primary subject or the photometrical value of thewhole capturing area measured by the distance-measuring sensors in astructure similar to the above.

The present embodiment describes the structure in which exposure isdetermined using the photometrical value of the primary subject measuredby using a part of at least one distance-measuring sensor and theaverage photometrical value of the whole capturing area measured by thephotometric sensors. The invention is not limited to the above case. Forexample, exposure can be determined using the photometrical value of theprimary subject measured by using a part of at least onedistance-measuring sensor and the photometrical value of the wholecapturing area measured by using the whole of the distance-measuringsensors.

According to the present embodiment, photometry and backlight detectionare included in automatic modes executed by the camera. For example, theinvention can also be applied to a structure in which distance-measuringsensors are used in spot photometry and the like.

As mentioned above, therefore, according to the first embodiment, in thesystem for detecting backlight using the AF sensors and the AE sensors,when the photometrical value obtained by the AE sensors is equal to orlarger than predetermined brightness, backlight detection is notperformed. In the system for detecting backlight using multi-point AFsensors and pattern AE sensors, when the photometrical value obtained byat least one AE sensor is equal to or larger than predeterminedbrightness, backlight detection is not performed. Consequently, thecamera, which can determine backlight without any inconvenience onphotographing condition close to the very limit of the photometricalrange, can be provided.

A wide-angle field distance-measuring camera according to a secondembodiment will now be described hereinbelow.

FIG. 8 is a diagram of the structure of a distance-measuring device inthe wide-angle field distance-measuring camera according to the presentembodiment. FIGS. 9, 10, and 11 are diagrams showing setting examples ofmonitor areas and calculation areas in the distance-measuring device inFIG. 8. FIG. 12 shows a photographing scene of the wide-angle fielddistance-measuring camera according to the second embodiment. FIGS. 13and 14 show subject data thereof. FIG. 15 is a diagram of a monitorcircuit of the distance-measuring device in FIG. 8.

Referring to FIG. 8, the distance-measuring device of the wide-anglefield distance-measuring camera according to the present inventioncomprises: a pair of reception lenses 101 a and 101 b for formingsubject images on a pair of line sensors 102 a and 102 b; the linesensors 102 a and 102 b for photoelectrically converting the subjectimages formed through the reception lenses 110 a and 101 b into electricsignals in accordance with the intensity of light and generating theelectric signals; integral control means 103 comprising an integralcontrol circuit for controlling integral action by the line sensors 102a and 102 b; an A/D conversion circuit 104 for analog-to-digitalconverting the analog electric signals generated from the line sensors102 a and 102 b into digital signals; monitor control means 105 whichincludes monitor means for monitoring subject-brightness informationduring the integral action, sets a monitor area, and generates a monitorsignal; and a CPU 106 for generating various control signals andperforming various calculations such as calculation regarding acamera-to-subject distance and the like. The CPU 106 constitutescalculation means and low-brightness-area determination means accordingto the present invention.

As shown in FIG. 15, the monitor control means 105 comprises:comparators 141 a 1 to 141 an and 141 b 1 to 141 bn; input changeoverswitches 142 a 1 to 142 an and 142 b 1 to 142 bn; and an OR circuit 143for outputting a monitor signal. Output terminals of the line sensors102 a are connected to respective input terminals of the comparators 141a 1 to 141 an. A reference voltage VREF is applied to the other inputterminal of each of the comparators 141 a 1 to 141 an. Output terminalsof the line sensor 102 b are connected to respective input terminals ofthe comparators 141 b 1 to 141 bn. The reference voltage VREF is appliedto the other input terminal of each of the comparators 141 b 1 to 141bn. Further, output terminals of the comparators 141 a 1 to 141 an areconnected to input terminals of the OR circuit 143 through the inputchangeover switches 142 a 1 to 142 an, each of which can switch betweenthe corresponding output terminal and a GND terminal. Output terminalsof the comparators 141 b 1 to 141 bn are connected to other inputterminals of the OR circuit 143 through the input changeover switches142 b 1 to 142 bn, each of which can switch between the correspondingoutput terminal and a GND terminal.

The comparators 141 a 1 to 141 an and 141 b 1 to 141 bn each output asignal at an H (high) level when an integral voltage input from thecorresponding line sensor 102 a or 102 b is equal to or lower than thereference voltage V_(REF). The input changeover switches 142 a 1 to 142an and 142 b 1 to 142 bn each switch between the output terminal of thecorresponding comparator 141 and the GND terminal. Switching isperformed due to a monitor setting signal in monitor setting, so thatthe input changeover switches 142 a 1 to 142 an and 142 b 1 to 142 bnare connected to the respective output terminals of the comparators 141a 1 to 141 an and 141 b 1 to 141 bn. The OR circuit 143 outputs amonitor signal. When an integral voltage of any one of sensors set tomonitor is equal to or less than VREF, the OR circuit 143 outputs asignal at an H (high) level.

A distance-measuring method of the wide-angle field distance-measuringcamera according to the second embodiment of the present invention willnow be described in brief with reference to the structure shown in FIGS.8 and 15.

Subject images formed by the reception lenses 101 a and 101 b aresubjected to the integral action on the line sensors 102 a and 102 b bythe integral control means 103 while a monitor area 111 is set to a widerange of each line sensor as shown in FIG. 9 (the integral action willbe referred to as first integral hereinbelow). An operation(hereinbelow, referred to as first calculation) to obtaincamera-to-subject distance data is executed every calculation area setshown by reference numerals 112 to 116 in FIG. 9 on the basis of sensordata obtained by the first integral. Generally, data to be used inphotographing is selected from the camera-to-subject distance dataobtained in the respective calculation areas 112 to 116 by apredetermined selection method such as well-known closest selection.

Specifically, in distance-measuring in a backlight scene as shown inFIG. 12, a monitor area 133 is set and the first integral is performed.When the image of a person as a primary subject has relatively lowerbrightness and lower contrast against a background as shown by sensordata 132 in FIG. 13 (sensor data 132 is larger than a threshold line136), a monitor area 135 is set in the area, where the low brightnessand the low contrast are determined in the first integral, and integralaction is then performed to this area as shown in FIG. 14 (the integralaction will be referred to as second integral hereinbelow). As shown inFIG. 10, on the basis of sensor data 134 obtained by the secondintegral, a monitor area 117 is set and a calculation area 118 is set tothe same range as the set monitor area 117 to obtain camera-to-subjectdistance data (hereinbelow, referred to as second calculation). On thebasis of the data obtained by the first calculation and the dataobtained by the second calculation, data to be used in photographing isselected by the selection method such as the foregoing well-knownclosest selection. For the area used in the second calculation, as shownin FIG. 11, monitor areas 120 to 122 can be set so as to include amonitor area 119 for the second integral.

In a camera having a taking lens (wide-angle lens) whose focal length isshort, however, each of the line sensors is used from end to end in somecases because the angle of view of the taking lens is large and theangle of view of AF is also set to be large in accordance with the aboveangle of view. In this case, when a uniform brightness area ismonitored, data obtained as being determined “dark” through theperipheral segments of the sensors is generated as shown in FIG. 24 dueto a deterioration in the performance of the reception lenses for the AFsensors or a degradation in the sensitivity of the sensors. Accordingly,if it is determined using only the threshold line 136 in FIG. 13 thatdata obtained by the peripheral segments of the sensors indicates lowerbrightness and lower contrast than those obtained by the centralsegments thereof (the data obtained by the peripheral segments is higherthan the threshold line 136), incorrect determination may be made.

In order to prevent the incorrect determination, a threshold line 137for data of the peripheral segments is set in the vicinity of thethreshold line 136, thus preventing incorrect determination of lowbrightness and low contrast due to the influence of the deterioration inthe performance of the reception lenses or the degradation in thesensitivity of the sensors. In this instance, the threshold line 137 isused to determine that areas “B” and “C” shown in FIG. 13 indicate lowbrightness and low contrast.

In a case where the area of low brightness and low contrast based onsensor data obtained by the first integral is narrower than apredetermined range, when a subject in the area includes a person, theperson exists far away. Accordingly, camera-to-subject distance data canbe obtained by only the first calculation. When the subject is not aperson, the subject actually has low brightness and low contrast. Whenthe second integral is performed, the effect thereof is not derived. Inthis case, therefore, the second integral is not performed.

The distance-measuring operation of the wide-angle fielddistance-measuring camera according to the second embodiment of thepresent invention will now be described in detail. FIGS. 16 and 17 showexamples of a method of setting a monitor area. FIG. 18 is a flowchartof the procedure of a distance-measuring sequence.

As shown in FIG. 18, in step S301, a monitor area for the first integralis set. Specifically, as shown in FIG. 16, when the number of sensorsegments of each line sensor is, for example, “16” and all of the sensorsegments are set so as to monitor, a sensor segment “D” in FIG. 16 isset to a reference and “1” is set to each bit of monitor setting data(monitor setting data=FFFFH). If eight central sensor segments are setso as to monitor, as shown in FIG. 17, a sensor segment “E” in FIG. 17is set to a reference and “1” is set to each of eight bits of monitorsetting data (monitor setting data=OFFOH). When the data is transferredto the monitor control means 105 by the CPU 106 shown in FIG. 8 in aserial communication manner, the monitor control means 105 controls theforegoing input changeover switches 142 a 1 to 142 an and 142 b 1 to 142bn shown in FIG. 15 on the basis of the above-mentioned data to set amonitor area.

In step S302, on the basis of photometrical data and a pre-integralresult, the sensitivity of the sensors for the first integral is set.The sequence proceeds to step S303. The sensitivity of the sensors canbe switched between two levels of low sensitivity and high sensitivityor can also be switched between multiple levels larger than two levels.

In step S303, the first integral is performed using the monitor area andthe sensitivity of the sensors set in steps S301 and S302. Then, thesequence proceeds to step S304. The first integral can be controlled inthe following manner. A monitor signal at an H (high) level output fromthe monitor circuit as shown in FIG. 15 is detected to terminate theintegral. Alternatively, an output integral voltage is evaluated in theCPU 106 using such monitor means that outputs an integral voltage of asensor segment whose integral speed is the highest among those of thesensor segments in the monitor area as a monitor signal. On the basis ofa result of the evaluation, the integral is terminated.

In step S304, subject signals obtained by the first integral in stepS303 are A/D converted into digital signals by the A/D conversioncircuit 104 shown in FIG. 8. The digital signals are read as sensor datainto a RAM (not shown) in the CPU 106. In this instance, the maximumvalue MAX (sensor data obtained by integrating the darkest portion) ofsensor data is also detected. After that, the sequence proceeds to stepS305.

In step S305, the predetermined calculation areas 112 to 116 are set asshown in FIG. 9 mentioned above. The sequence proceeds to step S306. Theset areas are not limited to those. The number of areas and the rangecan be changed depending on the specification of a camera, photographingconditions, and a mode.

In step S306, camera-to-subject distance data is obtained for everycalculation area set in step S305 by predetermined correlationcalculation and interpolation calculation and the like. The sequenceproceeds to step S307. In step S307, whether the sensor segment, whichoutputs the value MAX of sensor data read in the RAM in step S304,corresponds to the area “A” in FIG. 13 mentioned above is determined. Ifthe sensor segment corresponds to the area “A”, the sequence proceeds tostep S308. The above-mentioned threshold line 136 is selected shown inFIG. 13. Then, the sequence proceeds to step S310. On the other hand, ifthe sensor segment corresponds to the area “B” or “C” other than thearea “A” in the foregoing determination in step S307, the sequencebranches to step S309. The foregoing threshold line 137 in FIG. 13 isselected. Then, the sequence proceeds to step S310.

In step S310, whether the maximum value MAX of the sensor data detectedin step S304 is larger than a predetermined value (namely, whether thevalue MAX is higher than the threshold line 136 or 137) is determined.If the value MAX is larger than the predetermined value, the sequenceproceeds to step S311. If the value MAX is smaller than thepredetermined value, it is determined that the sensor data does notindicate low brightness. The sequence skips to step S319.

In step S311, whether the sensor data obtained by the first integral instep S303 includes an area indicating low brightness and low contrast isdetermined. Then, the sequence proceeds to step S312. In step S312,whether there is an area indicating low brightness and low contrast isdetermined on the basis of the determination in step S311. If YES, thesequence proceeds to step S313. If NO, the sequence skips to step S319.

In step S313, on the basis of a result of the determination in stepS311, a monitor area for the second integral is set. As shown in FIG.13, if the sensor data 132 indicating that the image of a person as aprimary subject has low brightness and low contrast is obtained in thefirst integral in which the monitor area is set to the range 133, themonitor area for the second integral is set to the range correspondingto the monitor area 135 shown in FIG. 14. For setting of the monitorarea, in a manner similar to the setting method described in step S301,“1” is set to each bit of monitor setting data corresponding to themonitor area 135, the set data is transferred to the monitor controlmeans 105 by the CPU 106 shown in FIG. 8, the monitor control means 105controls the input changeover switches 142 a 1 to 142 an and 142 b 1 to142 bn shown in FIG. 15 to set the monitor area. Then, the sequenceproceeds to step S314.

In step S314, on the basis of the maximum value MAX of the foregoingsensor data detected in step S304 and an average value of thelow-brightness low-contrast portion detected in step S311, thesensitivity of the sensors for the second integral is set. The sequenceproceeds to step S315. In step S315, the second integral is performedusing the monitor area and the sensitivity of the sensors set in stepsS313 and S314. The sequence proceeds to step S316. The second integralis controlled in a manner similar to step S303.

In step S316, subject image signals obtained by the second integral areA/D converted into digital signals through the A/D conversion circuit104 in FIG. 8. The digital signals are read as sensor data into the RAMof the CPU 106. The sequence proceeds to step S317. For the sensor datato be read, data of all the sensor segments can be read. Alternatively,only sensor data in a second calculation area set in step S317, whichwill be described hereinbelow, can be read.

In step S317, a calculation area for the second calculation is set. Thesequence proceeds to step S318. For an area to be set, as shown in FIG.10, an area can be set such that the monitor area 118 corresponds to thesame range as that of the monitor area 117. Alternatively, as shown inFIG. 11, a plurality of areas can be set such that the monitor areas 120to 122 correspond to the monitor area 119.

In step S318, camera-to-subject distance data is obtained for everycalculation area set in step S317 by predetermined correlationcalculation and interpolation calculation and the like. The sequenceproceeds to step S319. In step S319, camera-to-subject distance data tobe used in photographing is selected from the camera-to-subject distancedata obtained in steps S306 and S318 by the closest selection or thelike. The sequence is then returned.

The procedure of the sequence of determining low brightness and lowcontrast in step S311 will now be described in detail with reference toa flowchart of FIG. 19.

Referring to FIG. 19, in step S321, the head address of sensor datastored in the RAM of the CPU 106 in FIG. 8 is set. The sequence proceedsto step S322. In step S322, the number of sensor data stored in the RAMof the CPU 106 is set. The sequence proceeds to step S323. In step S323,F_LCON (low-contrast flag), ADR (head address data indicatinglow-brightness low-contrast area), and number n (the number of sensorsegments corresponding to the low-brightness low-contrast area) arecleared. The sequence proceeds to step S324.

In step S324, the sensor data with the address currently set in the RAMis read. The sequence proceeds to step S325. In step S325, thedifference between the maximum value MAX of sensor data detected in stepS304 in FIG. 18 and the sensor data read in step S324 is stored in theRAM (the difference will be referred to as “F” hereinbelow). Thesequence proceeds to step S326.

In step S326, low-contrast determination is performed. If the value “F”obtained in step S325 is larger than a predetermined value, it isdetermined that contrast is not low. The sequence proceeds to step S327.On the other hand, if “F” is smaller than the predetermined value, thesequence branches to step S336.

In step S327, whether previous sensor data indicates low contrast isdetermined. If F_LCON (low-contrast flag)=1, it is determined that thedata indicates low contrast. The sequence proceeds to step S328. IfF_LCON=0, it is determined that the data does not indicate low contrast.The sequence skips to step S331.

In step S328, whether the low-contrast area is larger than apredetermined range is determined. If the number of sensor segments ncorresponding to the low-brightness low-contrast area is larger than apredetermined value, it is determined that the area is larger than thepredetermined area. The sequence proceeds to step S329. If the number nis smaller than the predetermined value, it is determined that the areais smaller than the predetermined range. The sequence skips to stepS330.

In step S329, data indicating the head address ADR of the low-brightnesslow-contrast area and data indicating the number of sensor segments ncorresponding to the low-brightness low-contrast area are stored as dataindicating the low-brightness low-contrast area. The sequence proceedsto step S330. In step S330, the F_LCON and the number of sensor segmentsn corresponding to the low-brightness low-contrast area are cleared. Thesequence proceeds to step S331.

In this instance, if “F” obtained in step S325 is smaller than thepredetermined value in step S326, whether the previous sensor dataindicates low contrast is determined in step S336. If the F_LCON=0, itis determined that the data does not indicate low contrast. The sequenceproceeds to step S337. If the F_LCON=1, it is determined that the dataindicates low contrast. The sequence skips to step S338.

In step S337, the F_LCON is set. The RAM address of the current sensordata is stored in ADR serving as a head address of the low-brightnesslow-contrast area. The sequence proceeds to step S338. In step S338, 1is added to the number of sensor segments n corresponding to thelow-brightness low-contrast area. The sequence proceeds to step S331.

In step S331, a RAM address of sensor data to be read next is set. Thesequence proceeds to step S332. In step S332, whether the low-contrastdetermination for all of sensor data is completed is determined. If YES,the sequence proceeds to step S333. If NO, the sequence is returned tostep S324 to repeat steps S324 to S332.

In step S333, whether the last sensor data indicates low contrast isdetermined. If F_LCON=1, it is determined that the data indicates lowcontrast. The sequence proceeds to step S334. If F_LCON=0, it isdetermined that the data does not indicate low contrast. The sequence isreturned.

In step S334, whether the last low-contrast area is larger than thepredetermined range is determined. If the number n is larger than thepredetermined value, it is determined that the area is larger than thepredetermined range. The sequence proceeds to step S335. If the number nis smaller than the predetermined value, it is determined that the areais smaller than the predetermined range. The sequence is returned.

In step S335, in a manner similar to step S329, data of the head addressADR of the low-brightness low-contrast area and data indicating thenumber of sensor segments n corresponding to the low-brightnesslow-contrast area are stored as data indicating the low-brightnesslow-contrast area. Then, the sequence is returned.

As mentioned above, in the wide-angle field distance-measuring cameraaccording to the second embodiment of the present invention, even in thecase where a primary subject has lower brightness than that of abackground like a backlight scene, when a low-brightness low-contrastarea included in sensor data of the line sensors 102 a and 102 b isdetermined, determination is made using the two threshold lines 136 and137. The threshold line 136 is used for the central portion of each linesensor. The threshold line 137 is used for the peripheral portions ofthe line sensors. The threshold line 136 is lower than the thresholdline 137. Consequently, when the line sensors are used from end to endin determination, the determination is not influenced by the influenceof the deterioration in the performance of the reception lenses or thedegradation in the sensitivity of the sensors, thus preventing incorrectdetermination. Accordingly, enough contrast can be derived. The distanceto a primary subject can be measured with high accuracy. As mentionedabove, an area indicating relatively low brightness and relatively lowcontrast is detected in sensor data and a monitor area is set. Even whena primary subject exists in an area other than the center of a capturingarea, correct distance-measuring can be performed.

A wide-angle field distance-measuring camera according to a thirdembodiment of the present invention will now be described with referenceto FIGS. 20 and 22, etc.

FIG. 20 is a graph of output data of line sensors in the wide-anglefield distance-measuring camera according to the third embodiment. FIG.22 is a flowchart of the procedure of a distance-measuring sequence of adistance-measuring device in the wide-angle field distance-measuringcamera according to the third embodiment, the distance-measuringsequence using a threshold line as a high-order curve.

For the wide-angle field distance-measuring camera according to thethird embodiment, the structure of the distance-measuring device thereofand a method for setting a monitor area are substantially the same asthose shown in FIGS. 8 to 19 according to the second embodiment. Thethird embodiment differs from the second embodiment with respect to apoint that a high-order curve is used instead of the threshold lines 136and 137 shown in FIG. 13 used in the determination of whether a subjecthas lower brightness than that of a background. Accordingly, only thedifference therebetween will now be described. The explanation regardingthe content similar to that of the second embodiment is omitted.

In the case of the photographing scene as shown in FIG. 12, a monitorarea is set and the first integral is performed to obtain sensor data asshown in FIG. 20. Then, whether the image of a person as a primarysubject has low brightness is determined using a threshold line 160 as ahigh-order curve.

A distance-measuring sequence using the threshold line as a high-ordercurve will now be described with reference to FIG. 22.

For the procedure of the distance-measuring sequence shown in FIG. 22, aflow of steps S401 to S406 is similar to the flow of steps S301 to S306shown in FIG. 18 according to the second embodiment. Further, steps S408to S416 are also similar to steps S311 to S319 in FIG. 18.

Therefore, the difference between the sequences is only determination instep S407. If it is determined in step S407 that the maximum value MAXof the sensor data detected in step S404 is higher than the high-ordercurve 160 (ax^(n)+bx^(n−1)+ . . . +cx+d), the sequence proceeds to stepS408. If the value MAX is lower than the curve, it is determined thatthe sensor data does not include an area indicating low brightness. Thesequence skips to step S416. Reference symbol x in the expression of thecurve 160 denotes the sensor segment number. In FIG. 20, referencenumeral 163 denotes a monitor area and reference numeral 162 denotessensor output data.

As mentioned above, advantages similar to those of the second embodimentof the present invention can be obtained using the threshold line 160serving as the high-order curve.

A wide-angle field distance-measuring camera according to a fourthembodiment of the present invention will now be described with referenceto FIGS. 21 and 23.

FIG. 21 is a graph showing output data of line sensors in the wide-anglefield distance-measuring camera according to the fourth embodiment. FIG.23 is a flowchart of a distance-measuring sequence of adistance-measuring device in the wide-angle field distance-measuringcamera according to the fourth embodiment.

For the wide-angle field distance-measuring camera according to thefourth embodiment, the structure of the distance-measuring devicethereof and a method for setting a monitor area are substantially thesame as those shown in FIGS. 8 to 19 according to the second embodiment.The fourth embodiment differs from the second embodiment with respect toa point that before determination of whether a subject has lowerbrightness relatively than that of a background, sensor data iscorrected by the amount as much as the influence of a deterioration inthe performance of the reception lenses or a degradation in thesensitivity of the sensors, and the determination is then made usingonly one threshold line. Accordingly, only the difference therebetweenwill now be described.

In the case of the photographing scene as shown in FIG. 12, a monitorarea is set, and the first integral is performed as shown in FIG. 21.Then, in determination of whether the image of a person as a primarysubject has low brightness, the sensor data is corrected using sensordata, shown in FIG. 24, obtained when the sensors monitor an uniformbrightness area. The determination is made using a threshold line 170(predetermined value).

A distance-measuring sequence using the above sensor data will now bedescribed with reference to FIG. 23. For the procedure of thisdistance-measuring sequence, a flow of steps S421 to S424 is similar tothe flow of steps S301 to S304 shown in FIG. 18 according to the secondembodiment. Further, steps S426 and S427 are also similar to steps S305and S306 in FIG. 18. Steps S428 to S437 are also similar to steps S310to S319 in FIG. 18. Therefore, the difference between the sequences isonly the operation for correcting sensor data in step S425.

In step S425, as shown in FIG. 24 mentioned above, the sensor dataobtained when the sensors monitor a uniform brightness area is used.Sensor data is corrected using the sensor data obtained as mentionedabove. The sequence proceeds to step S426. In FIG. 21, reference numeral173 denotes a monitor area and reference numeral 172 denotes sensoroutput data.

As mentioned above, according to the fourth embodiment, even in a casewhere a primary subject has lower brightness than that of a backgroundlike a backlight scene, in determination of a low-brightnesslow-contrast area included in sensor data, this sensor data is correctedusing sensor data obtained when the sensors monitor a uniform brightnessarea. Consequently, the determination can be made using the thresholdline 170 (predetermined value). When each line sensor is used from endto end in determination, the determination is not influenced by adeterioration in the performance of the reception lenses and adegradation in the sensitivity of the sensors, thus preventing incorrectdetermination. Consequently, enough contrast can be obtained and thedistance to a primary subject can be measured with high accuracy. Asmentioned above, an area with relatively low brightness and relativelylow contrast is detected to set a monitor area. Consequently, when aprimary subject exists in an area other than the center of a capturingarea, the distance to the subject can be measured correctly.

As mentioned above, according to the second to fourth embodiments of thepresent invention, there can be provided a wide-angle fielddistance-measuring camera having a distance-measuring device, whereineven when each line sensor is used from end to end, the determination isnot influenced by a deterioration in the performance of the receptionlenses or a degradation in the sensitivity of the sensors so thatincorrect determination that a subject has low brightness and lowcontrast can be prevented. Accordingly, the distance-measuring devicecan measure a distance to a primary subject with reliabilityindependently of the condition of a background with higher brightnessthan that of the primary subject.

1. A wide-angle field distance-measuring camera having adistance-measuring device, the distance-measuring device comprising: apair of reception lenses for forming an image of a subject on a pair ofline sensors, wherein the pair of line sensors convert the subject imageformed by the reception lenses into electric signals in accordance withan intensity of light; integral control means for performing integralcontrol of the pair of line sensors; calculation means for calculatingdata corresponding to a camera-to-subject distance based on subjectimage data generated from the pair of line sensors; monitor means formonitoring subject-brightness information used in the integral control;monitor control means for setting a monitor area and outputting monitordata; and low-brightness-area determination means for determining a lowbrightness area included in output data of the line sensors inconsideration of an influence of one of (i) a deterioration inperformance of the reception lenses and (ii) a degradation insensitivity of the sensors, wherein the output data of the line sensorsis obtained by integration.
 2. The camera according to claim 1, whereinthe low-rightness-area determination means changes a threshold valueused in determination of the low brightness area in the output data in acentral portion of each line sensor and peripheral portions thereof. 3.The camera according to claim 1, wherein the low-brightness-areadetermination means approximates a threshold value used in determinationof the low brightness area in the output data of the line sensors with ahigh-order curve.
 4. The camera according to claim 1, wherein thelow-brightness-area determination means corrects the output data of theline sensors by an amount as much as the influence of one of (i) thedeterioration in the performance of the reception lenses and (ii) thedegradation in the sensitivity of the sensors, and then determines thelow brightness area.